Polyethylene terephthalate (PET fiber or polyester fiber) fiber has high breaking strength and elastic modulus, moderate resilience, excellent heat setting, good heat and light resistance, acid and alkali resistance and corrosion resistance since its inception. A series of excellent properties such as sex, and the fabric has the advantages of anti-wrinkle and capital-free, good rigidity, and is widely used in clothing, home textile and other fields.
However, due to the high crystallinity of PET, the structure is dense, and there is no functional group bonded to the dye on the molecular chain, so that the dye molecules are difficult to enter the fiber interior, and dyeing is difficult. It cannot meet the demand for bright, beautiful fabrics.
The reason why PET dyeing is difficult is that PET is a symmetrical linear macromolecule. The molecular chain does not contain a side chain group. The regularity is very good. Its main chain contains a rigid benzene ring and a flexible hydrocarbon group, and directly with the benzene ring. The linked ester group and the benzene ring form a rigid conjugated system, which restricts the free rotation of the flexible segment. This structure increases the wall ridge of the movement of the molecular segment, resulting in a higher glass transition temperature of PET, which needs to promote the diffusion of dye molecules into the fiber inside under high temperature conditions, and complete the dyeing step. In addition, PET has a regular molecular chain, good crystallinity, tight molecular chain arrangement, and no polar groups on the molecular chain that interact with dye molecules, making PET fiber coloring more difficult.
Therefore, the dyeing of the usual PET fiber is generally selected under the high temperature and high pressure, and the disperse dye is selected. When the temperature reaches the glass transition temperature of the PET fiber, the degree of free volume increase is small, the dyeing rate is not high, and the dyeing property is poor. Therefore, the energy consumption and low dye uptake caused by the high temperature and high-pressure method are the main problems now facing. In addition, PET fibers have a high melt viscosity, which is not conducive to processing.